vertical propagation characteristics and seasonal ... · vertical propagation characteristics and...

Ann. Geophys., 24, 2877–2889, 2006www.ann-geophys.net/24/2877/2006/© European Geosciences Union 2006

AnnalesGeophysicae

Vertical propagation characteristics and seasonal variability of tidalwind oscillations in the MLT region over Trivandrum (8.5 ◦ N, 77◦ E):first results from SKiYMET Meteor Radar

V. Deepa, G. Ramkumar, M. Antonita, K. K. Kumar, and M. N. Sasi

Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum 695022, India

Received: 13 January 2006 – Revised: 20 September 2006 – Accepted: 19 October 2006 – Published: 21 November 2006

Abstract. Tidal activity in the Mesospheric Lower Ther-mosphere (MLT) region over Trivandrum (8.5◦ N, 77◦ E)is investigated using the observations from newly installedSKiYMET Meteor Radar. The seasonal variability and ver-tical propagation characteristics of atmospheric tides in theMLT region are addressed in the present communication.The observations revealed that the diurnal tide is more promi-nent than the semi/terdiurnal components over this latitude.It is also observed that the amplitudes of meridional com-ponents are stronger than that of zonal ones. The amplitudeand phase structure shows the vertical propagation of diur-nal tides with vertical wavelength of∼25 km. However, thevertical wavelength of the semidiurnal tide showed consid-erable variations. The vertical propagation characteristics ofthe terdiurnal tide showed some indications of their generat-ing mechanisms. The observed features of tidal componentsare compared with Global Scale Wave Model (GSWM02)values and they showed a similar amplitude and phase struc-ture for diurnal tides. Month-to-month variations in the tidalamplitudes have shown significant seasonal variation. Theobserved seasonal variation is discussed in light of the varia-tion in tidal forcing and dissipation.

Keywords. Meteorology and atmospheric dynamics (Mid-dle atmosphere dynamics; Thermospheric dynamics; Wavesand tides)

1 Introduction

Atmospheric tides are the strongest perturbations that playa decisive role in controlling the dynamics of the MLT re-gion. By now, it is well established that atmospheric tidesare global oscillations with a period of a solar day and itssubharmonics. It is also known that they are excited by so-

Correspondence to:G. Ramkumar([email protected])

lar heating of water vapor in the troposphere and ozone inthe stratosphere. By realizing the importance of tidal ac-tivity, extensive wind observations in the MLT region havebeen carried out across the globe to explore its structure anddynamics (Tetenbaum et al., 1986; Avery et al., 1989; Man-son et al., 1988; Portnyagin et al., 1992; Fraser et al., 1995;Tsuda et al., 1999; Zhang et al., 2004). Extensive studieshave been carried out on tidal oscillations in the middle andhigh latitudes, whereas studies from the low-latitude MLT re-gion are very limited (Reddi et al., 1993; Reddi and Ramku-mar, 1997; Chang and Avery, 1997; Gurubaran and Ra-jaram, 1999). Most of these studies showed that the migrat-ing tides are prominent components in the MLT region andthere is considerable latitudinal variation in the tidal struc-ture. The high-latitude observations showed that the semidi-urnal component is more prominent than the diurnal compo-nent, whereas tropical latitude observations revealed that thediurnal component is stronger (Pancheva et al., 2002; Man-son et al., 1999, 2002a). To date, various platforms have beenused to study the MLT region winds and among these plat-forms, MF and meteor radar observations significantly con-tributed to our present understanding of tidal structure andits variability. However, these observations were unable toprovide a global picture of tidal activity in the MLT region.In an attempt to divulge the global aspects of tides, PlanetaryScale Mesopause Observing System (PSMOS) campaign hasbeen carried out (Pancheva et al., 2002). Even though theseobservations have revealed a great deal about various tidalmodes in the MLT region, the deployment of ground-basedinstruments is limited by the geography, such as oceanic re-gions. There were 22 radars included in the campaign, butthe network was not uniformly distributed, and represen-tation of tropical stations was rather sparse. However, bythe introduction of satellite observations of mesosphere andlower thermosphere neutral winds, a global coverage on theatmospheric tides in the MLT region was obtained. Mea-surements using the HRDI and WINDII onboard UARS have

Published by Copernicus GmbH on behalf of the European Geosciences Union.

2878 V. Deepa et al.: First results from SKiYMET Meteor Radar

Table 1. System specification of SKiYMET Meteor Wind Radar atTrivandrum (8◦ N, 77◦ E).

System specifications

Peak power 40 kWFrequency 35.25 MHzPRF 2144 HzPulse width 13.3µmTX antenna Four circular polarized 3-element Yagi

(crossed elements) at the corners of a squareRX antenna Five circular polarized 2-element Yagi

(crossed elements) spaced to form aninterferometer

provided a better understanding of the global picture of tides(Morton et al., 1993; Burrage et al., 1995a, b; McLandresset al., 1996; Manson et al., 1999, 2002a, b; Zhang et al.,2004). The HRDI gives night-time wind data at 95 km only(Talaat and Lieberman, 1999). But WINDII provides day-time green-line observations four times per week and nightmeasurements twice per week. In practice, several monthsof data are required to provide adequate local time coverage(Mc Landress et al., 1996; Hagan et al., 1997). Zonal aver-aging is also done to extract tidal information (Mc Landaresset al., 1996). Thus satellite measurements provide only anaverage picture of tidal oscillations.

A significant modeling effort has been made to understandthe mean global variation of tidal components (Forbes andVial, 1989; Hagan, 1996; Hagan et al., 1999; Hagan andRoble, 2001; Hagan and Forbes, 2002, 2003). Hagan etal. (1995) developed the two-dimensional, linearized, steady-state numerical tidal model, known as the Global Scale WaveModel (GSWM). Some of the above-discussed studies madean effort to compare the observed tidal features with themodel values. Chang and Avery (1997) made a detailedstudy on tidal activity and compared their observations withGSWM. They attributed the discrepancy in the comparisonsto the effects of nonmigrating tides. Most of the other com-parison studies reported impressive agreement between themodels and observations of tidal phases. But there are dis-turbing differences in tidal amplitudes, especially that theseasonal and latitudinal variability of tidal amplitudes haveshown considerable disagreement with the model values.

It is clear from the above discussion that the large degreeof tidal variability and the limited available observations,even with the UARS coverage, makes the establishment of acomplete tidal climatology very difficult to achieve. To over-come these difficulties a greater number of uniformly dis-tributed networks of ground station observations across theglobe are needed. Realizing the importance of these stud-ies, a state-of-the-art meteor wind radar has been installed atTrivandrum (8.5◦ N, 77◦ E) to continue the efforts of explor-ing the MLT region dynamics.

In the present study, the month-to-month variation of ver-tical characteristics of atmospheric tides in the MLT region,using the all-sky interferometric meteor (SKiYMET) radarat the low-latitude station Trivandrum (8.5◦ N), is presented.The horizontal wind observations from the radar system areused for the tidal analysis and to study its seasonal vari-ability. These are the initial results from the radar obser-vations, which are compared with GSWM02 (Hagan andForbes, 2002, 2003) model values. This study serves to as-sess the present understanding of the tidal characteristics inthe low-latitude MLT region and to compare the GSWM02values with the observations over this latitude.

In Sect. 2 the data analysis and system details are de-scribed. The results are discussed in Sect. 3. A summaryand conclusions are given in Sect. 4.

2 Data and method of analysis

The wind observations from the SKiYMET Meteor WindRadar, which became operational from June 2004, areused for the present study. This radar system operates at35.25 MHz, with a peak power of 40 kW, and is the mostpowerful radar of its kind. The system specifications aregiven in Table 1. A special transmitting scheme has beenworked out to avoid the echoes from the Equatorial Elec-tro Jet (EEJ). Four transmitting antennas at the corners of asquare are employed for this purpose. One pair of antennastransmits out of phase with the other, such that a null fieldwill be formed at the overlapping region of the beams, thusavoiding echoes from the EEJ region. Five separate receiversare used for data acquisition, one for each antenna. This al-lows interferometry to be performed in order to determinethe position of the meteor trail in the sky, without ambigui-ties in the angle of arrival. The radar system utilizes state-of-the-art software and computing techniques to acquire, de-tect, analyze and display meteor entrance events. By observ-ing how the meteor trail drifts with time, deductions can bemade about the speed and direction of the atmospheric windat the altitude at which the meteor was observed. The instru-ment detects a sufficient number of meteor echoes through-out the day, to derive a comprehensive picture of the windfield. Analysis of the decay time of the meteor trail allowsthe determination of absolute measurements of mesospherictemperatures. Radial velocity can be measured with an accu-racy of 5% or better and temperature with 10 K or better.

The horizontal wind is obtained by measuring the radialvelocity of every meteor detected and then combining thesemeasurements in an all-sky manner. Radial velocities aredetermined by using both auto- and cross-correlation func-tions associated with meteor detections, and using the rateof change of phase near zero lag to determine the radial ve-locity (Hocking et al., 2001). The horizontal wind data atevery hour with an altitude resolution of∼3 km in the 80–100 km altitude region is used for the present study. All zonal

Ann. Geophys., 24, 2877–2889, 2006 www.ann-geophys.net/24/2877/2006/

V. Deepa et al.: First results from SKiYMET Meteor Radar 2879

21

6 12 18 24 30 36 42 48 54 60 66 72

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Fig. 1. Time-he

consecutive days (72 hours). Red contours represents the westerly winds and green the

easterly winds.

Fig. 2. Time-height contour of the meridional wind observed during three consecutive

days (72 hours). Red contours represents the southerly winds and green the northerly

winds.

Fig. 1. Time-height contour of the zonal wind observed during threeconsecutive days (72 h). Red contours represent the westerly windsand green the easterly winds.

and meridional velocities in a month are averaged in hourlybins, at each altitude, to form a 30-day-based composite di-urnal cycle. This composite cycle provides a better repre-sentation of the tidal structure for a particular month, thana single day or 10-day diurnal cycle. The composite diur-nal cycles are obtained for every month from June 2004 toMay 2005 and subjected to Fourier analysis, to obtain thealtitude structure of amplitudes and phases of different tidalcomponents. The following section describes the results ob-tained from the present analysis. From the vertical profilesof amplitude and phase, vertical propagation characteristicsof tidal oscillations can be studied.

3 Results and discussion

Figures 1 and 2 show the time height variation of zonal andmeridional winds for three consecutive days, i.e. from 1 to3 July 2004. The red contours represent the westerly andsoutherly winds and green that of the easterly and northerly.These figures clearly reveal the presence of a diurnal tide inthe present observations. The wind contours tilt downwardwith increasing time, indicating the upward propagation ofthe wave energy, which is more clear in the case of merid-ional winds.

3.1 Diurnal tides

Figure 3 represents the altitude profiles of amplitude andphase of zonal diurnal tide for all the months, along with theGSWM02 model values (Hagan and Forbes, 2002, 2003).The GSWM02 is a 2-D model that employs observed dis-tributions of background winds (from HRDI data), temper-atures (MSISE 90 model), ozone (HALOE) and water va-por. It includes dynamical processes, such as eddy diffusionand gravity wave drag. In this model nonmigrating compo-

21

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igh

t (k

m)

-90

-70

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90

Meridional Wind(m/s)

Fig. 1. Time-height contour of the zonal wind observed during three

consecutive days (72 hours). Red contours represents the westerly winds and green the

easterly winds.

Fig. 2. Time-height contour of the meridional wind observed during three consecutive

days (72 hours). Red contours represents the southerly winds and green the northerly

winds.

Fig. 2. Time-height contour of the meridional wind observed duringthree consecutive days (72 h). Red contours represent the southerlywinds and green the northerly winds.

nents of tidal oscillations are also taken into account. Theheight profiles of amplitude show an increasing trend withheight during all the months except for June. The observedamplitudes are in the range of 10 to∼60 ms−1. The stan-dard error in the amplitude measurement is in the range 0.1–0.2 ms−1, whereas in phase it is∼0.1 h. Relatively low am-plitude values are observed during June, July, April and May,whereas amplitudes reaching up to 50–60 ms−1 are observedduring equinoxes, i.e. during September, October and March.These amplitude values are consistent with that observed byMc Landress et al. (1996) with WINDII data. The observedamplitudes are larger than that observed by Gurubaran andRajaram (1999) over a nearby location Thirunelveli (8.7◦ N,77.8◦ E). It can be noted that the amplitude of zonal wind re-mains more or less constant with height during June and July.During April and May the growth of amplitude with height isalso very weak. Studies over Christmas Island also showedthat during April, May and June the growth of the zonal windamplitude with height is very weak (Chang and Avery, 1997).The phase profiles show downward propagation with time,indicating upward wave energy flux. The phase values areconsistent with model values except for June, July and April.These phase profiles are used to estimate the vertical wave-lengths, which are found to be∼25 km. This wavelength isconsistent with that of the (1,1) mode of the migrating diur-nal tidal component (Forbes and Groves, 1987).

Figure 4 shows the altitude profiles of amplitude and phasefor meridional diurnal tides for different months. The ampli-tude of meridional diurnal tides is greater than that of zonalcomponent. The GSWM02 model values also show that overthis latitude the diurnal tidal amplitudes of the meridionalwind are larger than that of zonal winds. The observationsover other low latitude stations, such as Tirnelveli (8.7◦ N)(Gurubaran and Rajaram, 1999) and Christmas Island (2◦ N),(Chang and Avery, 1997; Manson et al., 1999; Tsuda et al.,

www.ann-geophys.net/24/2877/2006/ Ann. Geophys., 24, 2877–2889, 2006


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Fig. 3. Height profile of amplitude and phase of zonal diurnal tides from June 2004 to

May 2005. Squares represent the observed values and stars represent the GSWM02

model values.

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0 20 40 6080

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December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht(

km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100April 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

June 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

July 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100 November 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)

22

0 20 40 6080

84

88

92

96

100February 05

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)



model values.

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

October 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht(

km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100April 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

June 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

July 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100 November 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)

22

0 20 40 6080

84

88

92

96

100February 05

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)



model values.

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht(

km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100April 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

June 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

July 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100 November 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)

22

0 20 40 6080

84

88

92

96

100February 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)



model values.

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht(

km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100April 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

June 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

July 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100 November 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)

22

0 20 40 6080

84

88

92

96

100February 05

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)



model values.

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

October 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht(

km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100April 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

June 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

July 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100 November 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)

22

0 20 40 6080

84

88

92

96

100February 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)



model values.

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht(

km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100April 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

June 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

July 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100 November 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)

22

0 20 40 6080

84

88

92

96

100February 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)



model values.

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht(

km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100April 05

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

June 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

July 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100 November 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)

Fig. 3. Height profile of amplitude and phase of zonal diurnal tides from June 2004 to May 2005. Squares represent the observed values andstars represent the GSWM02 model values.

1999), also reported that the amplitude of the meridional di-urnal tide is greater than that of zonal diurnal component.The amplitude of meridional winds increases up to 90 kmand then decreases during June, April and May. DuringJuly the meridional wind amplitude decreases slightly withheight. Similar observations are seen over Christmas Islandwhich shows that the meridional wind amplitudes increaseto ∼50 ms−1, up to the altitude of 90 km and then decreasesduring April, May, June and July (Chang and Avery, 1997;Mansion et al., 1999). But the observations over Thirunelveli(Gurubaran and Rajaram, 1999) show that the diurnal tidalamplitudes decrease up to 90 km and then increases. Theamplitude and phase values are consistent with model val-

ues, except for the phase values during June, July, Decemberand January; the observed and model values of phase dur-ing these months differ by∼6 h. The vertical wavelength ofthe meridional diurnal component is also∼25 km, indicatingthat the observed diurnal tidal component is that of a (1,1)mode.

The vertical wavelength of the diurnal component calcu-lated by Chang and Avery is in the range of 50–100 km, incontrast to the present observation of∼25 km. The verti-cal wavelength of diurnal tides obtained by Gurubaran andRajaram (1999) over Thirunelveli is in the range of 40–50 km. Earlier observations at tropical stations, such as atArecibo, Puerto Rico (18◦ N), using incoherent scatter radar



23

Fig. 4. Same as fig. 3. but for meridional diurnal tides.

0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

23


0 20 40 6080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 6 12 18 24

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

July 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

August 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

September 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

October 04

Phase (hrs)0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

November 04

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

December 04

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

January 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 6 12 18 24

February 05

Phase (hrs)

0 20 40 6080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

March 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

April 05

Phase (hrs)0 20 40 60

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 6 12 18 24

May 05

Phase (hrs)

Fig. 4. Same as Fig. 3, but for meridional diurnal tides.

(Mathews, 1976; Harper, 1981; Zhang et al., 2004), and atPunta Borinquen, Puerto Rico (18◦ N) (Bernard et al., 1981),showed the dominance of diurnal tides with amplitudes rang-ing from 20 ms−1 to 35 ms−1 and vertical wavelengths from25 to 30 km in the 80–100 km height region. Their obser-vations showed that the amplitude of the meridional com-ponent is stronger than that of the zonal diurnal tide. Us-ing mesosphere-stratosphere-troposphere radar at Jicamarca,Peru (12◦ S) Countryman and Dolas (1982) observed strong24-, 12- and 8-h oscillations in the upper atmosphere, and thevertical wavelength of the 24-h component was observed tobe∼26 km, consistent with the present observations.

During all twelve months the meridional component leadsthe zonal wind, except at one or two heights in July and De-cember. Phase shifts (PS) between zonal and meridional di-

urnal tidal components varies with height and with month.During June and July the PS varies from∼9 h to ∼15 h inthe 80–100 km height range. The PS is∼3 h during August,November, January and February. During September, Oc-tober, and December, the PS is∼6 h, which indicates thatduring these months the zonal and meridional componentsare in quadrature polarization. From March to May the PSis ∼9 h up to 88 km and above that decreases to∼3.5 h. Thelarger amplitude and varying phase shifts between zonal andmeridional components indicate the presence of superposedmodes. Both zonal and meridional diurnal components dur-ing vernal equinox and summer have a significant phase dif-ference of 180◦ with that observed during autumnal equinoxand winter.



24

Fig. 5. Same as fig. 3. but for zonal semidiurnal tides.

0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)

Amplitude (ms-1)0 3 6 9 12

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 4 8 12

July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

24


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(hrs

)


September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100October 04

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


January 05

Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)-2 0 2 4 6 8 10

March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100May 05

Heig

ht

(km

)


Phase (hrs)

Fig. 5. Same as Fig. 3, but for zonal semidiurnal tides.

3.2 Semidiurnal tides

Figures 5 and 6 show the amplitude and phase profiles ofzonal and meridional semidiurnal tides for each month dur-ing the present observational period. The amplitude in-creases with height for both the components, as expectedduring all the months except for July, August and May, inthe case of the zonal component, where the amplitude valuesincrease up to 90 km and then decreases. During Septem-ber and January the amplitude values remain constant withheight. The rate of increase of amplitude with height variesfrom month to month. The growth of the zonal wind ampli-tude is larger during November, December, February, Marchand April (i.e. from 10 ms−1 at 82 km to 20 ms−1 at 98 km).

During other months the amplitude values increase from∼5 ms−1 at 82 km to∼10 ms−1 at 98 km. The amplitudeof the meridional component is greater than that of the zonalcomponent as observed in diurnal tidal amplitudes. The am-plitude of the meridional wind increases with height for allthe months. From July to October the rate of increase of am-plitude with height is larger and reaches a maximum valueof 30 ms−1 at 98 km. The observed amplitude values aregreater than that of the model values. These amplitude valuesare larger than that observed over Christmas Island (2◦ N) byMansion et al. (2002b). Observations at Christmas Islandshowed that monthly mean semidiurnal meridional ampli-tudes are in the range of 10–15 ms−1 (Burrage et al., 1995b).The amplitude values of semidiurnal tides observed over



25

Fig. 6. Same as fig. 3. but for meridional semidiurnal tides.

0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05

Heig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05

Heig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05

Heig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05H

eig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05

Heig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05

Heig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)Amplitude (ms

-1)0 4 8 12

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05H

eig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05

Heig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05

Heig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05H

eig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05

Heig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 3 6 9 12

October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05H

eig

ht

(km

)


Phase (hrs)

25


0 10 20 3080

84

88

92

96

100June 04

Heig

ht

(km

)


Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 3 6 9 12

July 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


August 04

Phase (hrs)

0 10 20 30 4080

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 81012

September 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 10 20 30

80

84

88

92

96

100 January 05

Heig

ht

(km

)


Phase (hrs)0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 10 20 3080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 10 20 30

80

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 10 20 30

80

84

88

92

96

100 May 05

Heig

ht

(km

)


Phase (hrs)

Fig. 6. Same as Fig. 3, but for meridional semidiurnal tides.

Arecibo (18◦ N), using incoherent scatter radar, is∼15 ms−1

(Zhang et al., 2004). The semidiurnal tidal amplitude ob-served using HRDI wind data at the latitude of∼20◦ N is∼25 ms−1 during April and May and is 20–25 ms−1 at theequator during June to August (Burrage et al., 1995b). Thus,the present observations show large, semidiurnal amplitudesin meridional winds as compared to other geographical loca-tions.

It is seen from Figs. 5 and 6 that the phase decreases withheight consistently for both zonal and meridional compo-nents. The phase structure is similar to that of GSWM02.The observed and model phase values differs by∼3 h dur-ing October, November and December for zonal winds. Forother months, observed and model phase values are in good

agreement. In the case of meridional winds the observed andmodel values of phase differ by∼4 h during June, July andAugust. The vertical wavelength calculated from the phasestructure shows variation from month to month. The verticalwavelength of the zonal wind is calculated to be∼100 kmfrom June to September. From October to May the verti-cal wavelength is∼64 km. For the meridional wind the ver-tical wavelength is∼100 km during January and February.During October to May it is found to be∼64 km. Duringother months still shorter vertical wavelengths, of the orderof 40–50 km, are estimated. The larger vertical wavelengths(>100 km) correspond to the vertical wavelength of the (2,2)symmetrical mode (Forbes, 1982). The higher order semid-iurnal components, such as (2,4), (2,5) or (2,7), have much



26

Fig. 7. Same as fig. 3. but for zonal terdiurnal tides.

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)

Amplitude (ms-1)0 2 4 6 8Phase (hrs)

0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

October 04

Phase (hrs)

26


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100August 04

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100 November 04

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100January 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


February 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs) 0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


May 05

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)

Fig. 7. Same as Fig. 3, but for zonal terdiurnal tides.

shorter vertical wavelength values. The present observationsshow that the (2,2) mode with wavelength∼100 km is gen-erally stronger in the zonal wind compared to other modes.Higher order modes show strong signatures in the meridionalwind during some months. Forbes (1982) reported that the(2,2) mode grows exponentially up to about 70 km and athigher altitudes its amplitude decreases due to dissipation.Above this altitude, higher order modes (2,4), (2,5) and (2,7)become more prominent. Present observations also show thesimilar signature and are thus consistent with the earlier stud-ies.

3.3 Terdiurnal tides

Figures 7 and 8 depict the vertical structure of the ampli-tude and phase of the terdiurnal tide for zonal and meridionalcomponents, respectively. The amplitude of the zonal terdi-urnal tide increases with height for all the 12 months. Thevalues increase from 5 ms−1 to 10 ms−1 for both zonal andmeridional winds. The maximum zonal wind amplitude ob-served is 22 ms−1 during July. The amplitude of meridionalwind increases with height except for July and October. Theamplitude of both the zonal and meridional winds increasesup to 95 km and then decreases during the month of October.Terdiurnal tides of amplitude 10 ms−1 in the zonal compo-nent and 5 ms−1 in the meridional component were reported



27

Fig. 8. Same as fig. 3. but for meridional terdiurnal tides.

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)


Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)


Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)


Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)


Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)


Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)


Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)


Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)Amplitude (ms

-1)0 2 4 6 8

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

27


0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


June 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


July 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)

Amplitude (ms-1)

0 2 4 6 8

August 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


September 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


October 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Heig

ht

(km

)


November 04

Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


December 04

Phase (hrs)0 5 10 15 20

80

84

88

92

96

100January 05

Heig

ht

(km

)


0 5 10 15 2080

84

88

92

96

100February 05

Heig

ht

(km

)


Phase (hrs)

0 5 10 15 2080

84

88

92

96

100

Heig

ht

(km

)


March 05

Phase (hrs)0 5 10 15 2080

84

88

92

96

100April 05

Heig

ht

(km

)


Phase (hrs)0 5 10 15 20

80

84

88

92

96

100

Phase (hrs)

Heig

ht

(km

)

Amplitude (ms-1)

-2 0 2 4 6 8

May 05

Fig. 8. Same as Fig. 3, but for meridional terdiurnal tides.

by Reddi and Ramkumar (1997) over Trivandrum. UsingHRDI wind data, Smith (2000) observed terdiurnal tide witha maximum amplitude at 20◦ latitude.

The phase of the zonal wind remains constant at∼8 h. Thevertical wavelength is found to be very large. The phase re-mains constant at∼6 h for meridional winds, during August,December, February and April as well, indicating a large ver-tical wavelength. During these months, zonal and meridionalcomponents are in almost quadrature polarization. DuringJune and August, the phase of the meridional component in-creases with height up to 95 km. During July, September,January and May the phase decreases with height, and thevertical wavelength is very short, i.e.∼16 km. The verti-

cal wavelength is∼50 km during October, November andMarch in the case of meridional winds. From the earlier ob-servations from Trivandrum, Reddi and Ramkumar (1997)reported strong terdiurnal oscillations with a very large verti-cal wavelength (>100 km) and a smaller vertical wavelengthof ∼20 km. Other observations of terdiurnal oscillations overtropical latitudes were reported by Bernald et al. (1981) overPuerto Rico (18◦ N), with a large vertical wavelength andsometimes as low as 50 km. Roper et al. (1993) also re-ported a significant amplitude of the terdiurnal oscillationover Arecibo.

Terdiurnal tides are produced by various physical pro-cesses, such as direct generation by solar thermal heating,



28

1 2 3 4 5 6 7 8 9 10 11 12

Time (months)

82

84

86

88

90

92

94

96

98

Heig

ht

(km

)

0

20

40

60

Zonal Diurnal Amplitude (m/s)

J J A S O N D J F M A M

1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98

He

igh

t (k

m)

0

15

30

45

60

Meridional Diurnal Amplitude (m/s)


Fig. 9. Time-height contours of zonal diurnal amplitude showing the seasonal variation

starting from June 2004 to May 2005. Contour intervals are 4 ms-1

.

Fig. 10. Same as Fig.9 but for meridional diurnal tide.

Fig. 9. Time-height contours of zonal diurnal amplitude showingthe seasonal variation starting from June 2004 to May 2005. Con-tour intervals are 4 ms−1.

nonlinear interaction between the diurnal and semidiurnaltides, and tidal/gravity wave interaction. Based on both the-oretical and observational studies Glass and Fellows (1975)and Teitelbaum et al. (1989) suggested that the terdiurnal tidecould be produced by the nonlinear interaction between diur-nal and semidiurnal tides. Miyahara and Forbes (1991) pre-sented quantitative time dependent calculations, demonstrat-ing that a diurnal tide can modulate the momentum deposi-tion of gravity waves into the meanflow and hence produce asecondary oscillation near the 8-h and 12-h periods.

Classical or linear tidal oscillations are treated theoreti-cally as first order perturbations, which are forced by solarheating. The solar driven or linear terdiurnal tides have largevertical wavelengths (Teitelbaum et al., 1989). Higher ordereffects are forced by combination of the primary wave field.The nonlinear mixing of diurnal and semidiurnal oscillationsgives (Thayapparan, 1997)

u ∝ cos[2π

(1

T12+

1T24

)t − 2π

(1

λ12+

1λ24

)z + 81

]+

cos[2π

(1

T12−

1T24

)t − 2π

(1

λ12−

1λ24

)z + 82

],

(1)

whereu is the zonal or meridional wind,T the period,λ thewavelength,8 is the phase,t the time in hours. Among theforced waves, the one with the frequency and wavenumberequal to the sum of the frequencies and wavenumbers of thediurnal and semidiurnal tides is a terdiurnal tide. The otherwave with the frequency and wavenumber equal to the dif-ference of the frequencies and wavenumber of the diurnaland semidiurnal tides is a secondary diurnal tide. When adiurnal tide with vertical wavelengthλ1, nonlinearly interactwith a semidiurnal tide of vertical wavelengthλ2, propagat-ing in the same direction, a terdiurnal tide of vertical wave-lengthλz=λ1λ2/(λ1+λ2) is produced (Reddi and Ramkumar,1997). The observed vertical wavelength of the zonal andmeridional diurnal tide in the present study is∼25 km. The

28

1 2 3 4 5 6 7 8 9 10 11 12

Time (months)

82

84

86

88

90

92

94

96

98

Heig

ht

(km

)

0

20

40

60

Zonal Diurnal Amplitude (m/s)


1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98

He

igh

t (k

m)

0

15

30

45

60

Meridional Diurnal Amplitude (m/s)


Fig. 9. Time-height contours of zonal diurnal amplitude showing the seasonal variation

starting from June 2004 to May 2005. Contour intervals are 4 ms-1

.

Fig. 10. Same as Fig.9 but for meridional diurnal tide.

Fig. 10. Same as Fig. 9 but for meridional diurnal tide.

observed vertical wavelength of the meridional semidiurnaltide varies from∼40 km to 64 km. The vertical wavelengthcalculated for the terdiurnal tide, using the above equation,varies from 15 km to 25 km and the observed vertical wave-length of the meridional terdiurnal tide varies from 15 km to50 km. The calculated and observed vertical wavelength ofthe meridional terdiurnal tide is in good agreement duringSeptember and May. During all the other months the ob-served vertical wavelength is 2–3 times larger than the cal-culated value for the nonlinearly generated terdiurnal tide,except for January. This result thus shows an observationalevidence of a possible nonlinear interaction between the diur-nal and semidiurnal tides during some of the months. But thevertical wavelength of the zonal terdiurnal tide is observed tobe very large during all the 12 months. This suggests otherpossibilities of terdiurnal tidal generation, such as direct so-lar heating, tidal/gravity wave interaction and changes in theexcitation sources in the lower atmosphere.

3.4 Seasonal variation

Figure 9 shows the time-height section of the diurnal tidalamplitudes for zonal winds. The seasonal variation of tidalactivity in the MLT region is clearly revealed from this fig-ure. The tidal amplitudes show maximum activity above90 km. The maximum value is observed during September,October, February and March, i.e. during the autumnal andvernal equinox. Earlier observations also showed that diur-nal tides maximize over low latitudes and are strongest inthe equinoxes (Burrage et al., 1995a, b; Mc Landress et al.,1996; Reddi and Ramkumar, 1997; Gurubaran and Rajaram,1999). Figure 10 shows the seasonal variation of diurnaltidal amplitudes for meridional winds. In meridional windas well, the maximum tidal activity is observed above 90 km.The enhanced activity is observed during December–January(winter). During June and July (summer), maximum merid-ional amplitudes are observed below 90 km. The diurnal tidal



29

1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98

Heig

ht

(km

)

0

5

10

15

20

25

Semidiurnal Zonal Amplitude (m/s)


1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98

Heig

ht

(km

)

0

5

10

15

20

25

Semidiurnal Meridional Amplitude (m/s)


Fig. 11. Same as Fig.9 but for zonal semidiurnal tide.

Fig.12. Same as Fig.9 but for meridional semidiurnal tide.

Fig. 11. Same as Fig. 9 but for zonal semidiurnal tide.

29

1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98H

eig

ht

(km

)

0

5

10

15

20

25

Semidiurnal Zonal Amplitude (m/s)


1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98

Heig

ht

(km

)

0

5

10

15

20

25

Semidiurnal Meridional Amplitude (m/s)


Fig. 11. Same as Fig.9 but for zonal semidiurnal tide.

Fig.12. Same as Fig.9 but for meridional semidiurnal tide.

Fig. 12. Same as Fig. 9 but for meridional semidiurnal tide.

amplitudes show signatures of semiannual variability. Haganet al. (1999) reported pronounced SAO in the meridional di-urnal wind amplitude observed by HRDI over 20◦ latitudeat 95-km altitude. They attributed this feature to seasonallyvarying gravity wave drag and eddy dissipation on the diurnaltide. They could reproduce the observed SAO in diurnal tidesusing the GSWM-98 model by including seasonally varyingforcing, dissipation and meanflow effects. Seasonal varia-tions of diurnal tides may be related to changes in the sourcestrengths, such as the latent heat release associated with trop-ical deep convective activity (Forbes et al., 1997; Hagan etal., 1997), gravity wave variances in the upper stratosphere,which are expected to play an important role in modulatingtidal amplitude (Wu and Jiang, 2005), or due to the nonlinearinteraction between quasi-stationary planetary waves and thetidal oscillation (Oberheide et al., 2005).

Figures 11 and 12 show the seasonal variation of the am-plitude of zonal and meridional semidiurnal tides. Maximumamplitudes are observed during December–March, i.e. win-

30

1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98

Heig

ht

(km

)

0

5

10

15

Terdiurnal Zonal Amplitude (m/s)


1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98

Heig

ht

(km

)

0

5

10

15

Terdiurnal Meridional Amplitude (m/s)


Fig. 13. Same as Fig.9 but for zonal terdiurnal tide.

Fig. 14. Same as Fig.9 but for merdional terdiurnal tide.

Fig. 13. Same as Fig. 9 but for zonal terdiurnal tide.

30

1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98

Heig

ht

(km

)

0

5

10

15

Terdiurnal Zonal Amplitude (m/s)


1 2 3 4 5 6 7 8 9 10 11 12

Time (month)

82

84

86

88

90

92

94

96

98

Heig

ht

(km

)

0

5

10

15

Terdiurnal Meridional Amplitude (m/s)


Fig. 13. Same as Fig.9 but for zonal terdiurnal tide.

Fig. 14. Same as Fig.9 but for merdional terdiurnal tide. Fig. 14. Same as Fig. 9 but for merdional terdiurnal tide.

ter and vernal equinox in the case of the zonal semidiurnaltide. The meridional semidiurnal tide shows maximum am-plitudes during June to September. Burrage et al. (1995a, b),using HRDI wind data, and McLandress et al. (1996), withWINDII data, observed that the semidiurnal variability in themeridional wind in the equatorial region is maximum fromApril to August, which is consistent with the present results.They also observed that the variability in zonal semidiurnalcomponent in the equatorial region is weak.

Seasonal variations of amplitude of zonal and meridionalterdiurnal tide are shown in Figs. 13 and 14, respectively.Maximum zonal terdiurnal amplitudes are observed in July,October, March and April. Meridional terdiurnal amplitudesare larger during October, November, January, February andMarch. The variability of the meridional terdiurnal compo-nent is similar to the meridional diurnal component. Thissupports the hypothesis that the terdiurnal component couldbe generated by the nonlinear interaction between the diurnaland semidiurnal tide or by diurnal tidal/gravity wave interac-tion.



4 Summary and concluding remarks

This paper reports the results from SKiYMET radar obser-vations at Trivandrum (8◦ N, 77◦ E) during June 2004–May2005. The diurnal tidal component is observed to be promi-nent throughout the period of observation. The amplitude ofthe meridional diurnal tide is stronger than that of the zonaldiurnal tide. The semidiurnal and terdiurnal tidal compo-nents are also found to be strong. The amplitude of the di-urnal components attains a maximum of∼50 ms−1, and thatof the semidiurnal and terdiurnal components are∼20 ms−1

and 10 ms−1, respectively. The phase structure of all threecomponents shows a decreasing trend with altitude, indi-cating vertical propagation. The observed amplitudes andphases of the diurnal and semidiurnal tides are comparedwith the GSWM02 model. The observed amplitudes areequal to or greater than the model values. The observed andmodel phase structures are similar.

The vertical wavelength of the diurnal tidal components isfound to be∼25 km. The observed features of the diurnalcomponents indicated the presence of the (1,1) mode. Thevertical wavelength of the semidiurnal tide is found to be>100 km, which indicates that the (2,2) mode is prominentlypresent. Sometimes higher order semidiurnal modes are alsoobserved, as indicated by smaller vertical wavelengths (40–50 km) during some months. The vertical wavelength of theterdiurnal tide suggests that the observed terdiurnal tides areproduced by various sources, such as direct solar heating,nonlinear interaction between diurnal and semidiurnal tides,and by tide/gravity wave interaction.

Prominent seasonal variation is observed in tidal charac-teristics. The diurnal tidal components are strong during twoequinoxes. Semidiurnal zonal tides are stronger during thewinter and vernal equinox, and meridional semidiurnal tidesare strong during the summer and vernal equinox. Zonalterdiurnal amplitudes are stronger during equinoxes. Merid-ional terdiurnal amplitudes are strong during the winter andvernal equinox. Observed seasonal variation of various tidalmodes can be attributed to the variation in the forcing anddissipation mechanisms. Detailed studies on these aspectswill be pursued with a larger database.

This is the most powerful SKiYMET radar operationalover the globe. The observations using this radar fromthe equatorial region will serve as an input to the globaltidal studies under the program “CAWSES” (Climate AndWeather of Sun Earth System).

Acknowledgements.The SKiYMET radar installed at SpacePhysics Laboratory was sanctioned under the 10th five year planof Department of Space, India. The authors would like to ac-knowledge the support and encouragement provided by Chairman,ISRO, Director, VSSC and Director, SPL for installing the radarat our laboratory. The contributions from the team of engineersfrom Genesis Software Pty. Ltd, Australia and W. K. Hocking, Mar-doc. Inc. Ltd., Canada, are well appreciated in successfully commis-sioning the radar facility. The authors are grateful to M. Hagan for

the GSWM02 values of tidal oscillations taken from website. Weacknowledge the services of M. Shajahan, M. Nair and Smt. L. Sar-ala for taking care of the system. The authors (V. Deepa and M. An-tonita) are thankful to ISRO for providing Research fellowships.

Topical Editor U.-P. Hoppe thanks two referees for their help inevaluating this paper.

References

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